Objective: Research suggests 25% to 35% of children with attention-deficit/hyperactivity disorder (ADHD) have comorbid anxiety disorders. This double-blind study compared atomoxetine with placebo for treating pediatric ADHD with comorbid anxiety, as measured by the ADHD Rating Scale-IV-Parent Version: Investigator Administered and Scored (ADHDRS-IV-PI) and the Pediatric Anxiety Rating Scale (PARS). Method: Patients (ages 8-17 years) meeting DSM-IV criteria for ADHD and generalized anxiety disorder, separation anxiety disorder, and/or social phobia were randomized to 12 weeks of atomoxetine (n = 87) or placebo (n = 89). ADHDRS-IV-PI and PARS total scores were analyzed using analysis of covariance last observation carried forward and repeated-measures analyses. Results: Sixty-six patients in each group completed the study. Mean ADHDRS-IV-PI total score improved significantly for atomoxetine (n = 55; -10.5, SD 10.6) relative to placebo (n = 58; -1.4, SD 8.3; p less than 0.001). Mean PARS total score also improved significantly for atomoxetine (n= 55; -5.5, SD 4.8) relative to placebo (n = 58; -3.2, SD 5.0; p = 0.011). Conclusions: Atomoxetine was efficacious in reducing ADHD symptoms in patients who have ADHD with comorbid anxiety and was well tolerated. There was also a significant reduction in independently assessed anxiety symptoms using both clinician-rated and self-rated measures, which merits further investigation. Results support consideration of atomoxetine for the treatment of ADHD in youths who have ADHD with comorbid anxiety disorder. (Contains 3 tables.)